In the normal sulfite pulping of wood the lignin and the greater part of the hemicellulose are dissolved, and sometimes also a minor part of the alpha cellulose is dissolved. A substantially pure alpha cellulose product may be desired, if the pulp has to be used for the manufacturing of viscose cellulose, but in the case of paper pulp the removal of the hemicellulose involves, as a rule, only a loss of yield.